This project is designed to determine the relationship between the physiological properties of individual motor units and certain key biochemical properties of the unit's constituent muscle fibers. A collaboration has been established between two laboratories, one engaged in quantitative single cell biochemistry, the other in spinal cord electrophysiology. The experimental approach is 1) to determine physiological characteristics of whole motor units, both nerve and muscle components, 2) to identify those units by a glycogen depletion technique, 3) to dissect segments of the identified unit fibers, and 4) to analyze these for selected metabolic enzymes. (The capability to identify motor unit fibers and to biochemically analyze single fibers from muscle cross-sections is a major advantage of this application.) The primary aim is to functionally correlate some aspects of energy metabolism with physiological properties of motor aspects of energy metabolism with physiological properties of motor units. In addition to the major purpose, it is expected that practical information will be gained about muscle fiber classification systems. The objectives of this work bear on a fundamental issue in neuromuscular interactions: the identity of the undelrying biochemical properties of muscle that govern its physiological capacity. The study of motor units has contributed importantly to this issu7e. The proposed study would refine our understanding of motor units. The ultimate health-related value of this work is to provide clues to the etiology of diseases which affect muscle performance.